<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
   <script>
    //    function User(name,pass){
    //        this.name=name
    //        this.pass=pass
    //    }
    //    User.prototype.showName=function(){
    //        alert(this.name)
    //    }
    //    User.prototype.showPass=function(){
    //        alert(this.pass)
    //    }
    //    function VipUser(name,pass,level){
    //        User.call(this,name,pass)
    //        this.level=level
    //    }
    //    VipUser.prototype=new User()
    //    VipUser.prototype.constructor=VipUser
    //    VipUser.prototype.showLevel=function(){
    //        alert(this.level)
    //    }

    class User{
        constructor(name,pass){
            this.pass=pass
            this.name=name
        }
        showName(){
            alert(this.name)
        }
        showPass(){
            alert(this.pass)
        }
    }
    class VipUser extends User{
        constructor(name,pass,level){
            super(name,pass)
            this.level=level
        }
        showLevel(){
            alert(this.level)
        }
    }
    var user=new VipUser('yan',1234,5)
    user.showName()
    user.showLevel()
   </script> 
</body>
</html>